Lens Dose Research Articles

Artifact-free CT images for electron beam therapy using a patient-specific non metallic shield

Patient’s CT images taken with metallic shields for radiotherapy suffer from artifacts. Furthermore, the treatment planning system (TPS) has a limitation on accurate dose calculations for high density materials. In this study, a Monte Carlo (MC)-based method was developed to accurately evaluate the dosimetric effect of the metallic shield. Two patients with a commercial tungsten shield of lens and two patients with a custom-made lead shield of lip were chosen to produce their non-metallic dummy shields using 3D scanner and printer. With these dummy shields, we generated artifact-free CT images. The maximum CT number allowed in TPS was assigned to metallic shields. MC simulations with real material information were carried out. In addition, clinically relevant dose-volumetric parameters were calculated for the comparison between MC and TPS. Relative dosimetry was performed using radiochromic films. The dose reductions below metallic structures were shown on MC dose distributions, but not evident on TPS dose distributions. The differences in dose-volumetric parameters of PTV between TPS and MC for eye shield cases were not clearly shown. However, the mean dose of lens from TPS and MC was different. The MC results were in superior agreement with measured data in relative dosimetry. The lens dose could be overestimated by TPS. The differences in dose-volumetric parameters of PTV between TPS and MC were generally larger in lip cases than in eye cases. The developed method is useful in predicting the realistic dose distributions around the organs blocked by the metallic shields.

EYE LENS DOSE OPTIMIZATION THROUGH GANTRY TILTING IN BRAIN CT SCAN: THE POTENTIAL EFFECT OF THE RADIOLOGICAL TECHNOLOGISTS' TRAINING.

This study was designed to evaluate the effect of the radiological technologists' training on optimising the eye lens dose in brain computed tomography (CT) examinations. The lens dose of 50 adult patients was measured using thermoluminescent dosimeters before and after technologists' training. Dose values of lenses, dose length product (DLP), volumetric CT dose index (CTDIvol) as well as image quality in terms of quantitative (contrast to noise ratio and signal to noise ratio) and subjective (artefact) parameters were compared before and after training. Lens dose values were 31.57±9.84mGy and 5.36±1.53mGy before and after training, respectively, which was reduced by ~83% (p<0.05). The values of DLP, CTDIvol and image quality parameters were not significantly different (p>0.05) and all images were diagnostically acceptable. Excluding the orbits from the scanning range is an efficient approach to optimize the lens dose; the training of the technologists has also a pivotal role in dose reducing.

Radiation protection of operators and patients in a hybrid Angio-MR suite

This work investigates the patient eye lens dose and x-ray scatter to the operator expected for a proposed hybrid Angio-MR concept. Two geometries were simulated for comparative assessment: a standard C-arm device for neuro-angiography applications and an innovative hybrid Angio-MR system concept, proposed by Siemens Healthineers. The latter concept is based on an over-couch x-ray tube and a detector inside an MRI system, with the aim of allowing combined, simultaneous MRI and x-ray imaging for procedures such as neurovascular interventions (including x-ray fluoroscopy and angiography imaging, 3D imaging, diffusion, and perfusion). To calculate the scattered radiation dose to the physician, Monte Carlo simulations were performed. Dose estimates of simplified models of the brain and eyes of both the patient and the physician and of the physician’s torso and legs have been calculated. A number of parameters were varied in the simulation including x-ray spectrum, field of view (FOV), x-ray tube angulation, presence of shielding material and position of the physician. Additionally, 3D dose distributions were calculated in the vertical and horizontal planes in both setups. The patient eye lens dose was also calculated using a detailed voxel phantom and measured by means of thermoluminescent dosimeters (TLDs) to obtain a more accurate estimate. Assuming the same number of x-rays and the same size of the irradiated area on the patient’s head, the results show a significant decrease in the scattered radiation to the physician for the Angio-MR system, while large increases, depending on setup, are expected to patient eye lens dose.

Clinical efficacy and molecular effects of lenvatinib (Len) and letrozole (Let) in hormone receptor-positive (HR+) metastatic breast cancer (MBC).

1019 Background: Preclinical studies show cross talk between RET and estrogen receptor, with at least additive treatment (Tx) effect of Len, a RET inhibitor, with Let. Our previous work concluded a recommended phase 2 dose (RP2D) of Len 14mg daily and Let 2.5mg daily (Lim, ASCO 2019). We present efficacy data from dose escalation and expansion cohorts. Methods: Safety, tolerability and efficacy data of MBC patients in both dose escalation (Len dose level 1 [DL]:20mg, DL -1:16mg and DL -2:14mg) and expansion (Len 14mg) cohort of this phase Ib/II study of combination Len+Let study was analysed. Patients were treated with single-agent Len for 2 weeks, followed by Len+Let until disease progression (PD). Serial tumor biopsies at baseline, after Len alone, 4 weeks post Len+Let, and upon PD, were sequenced for 440 genes with the ACTOnco+ platform. Results: A total of 33 pts (DL1 6pts, DL-1 6pts, DL-2 + expansion 21pts) with median 5 lines of prior Tx (range 0-11) were enrolled; 87.9%, 75.8%, and 75.8% had prior endocrine therapy (ET), ET+CDK4/6 inhibitor (i), and chemotherapy (CT) respectively. Objective response rate (ORR), disease control rate (DCR) ≥6 months (m), median duration of response (DOR), and percentage progression-free (PPF) at 12m were 33.3%, 45.5%, 11.5m (range 6.3-22.4), and 27.2% respectively. Among patients who previously progressed on CDK4/6i (n = 25), ORR, DCR ≥6m, median DOR, and PPF at 12m were 24.0%, 40.0%, 13.7m (range 6.3-18.2), and 12.0% respectively. Of note, 3/25 (12%) patients had durable response to Len+Let lasting ≥12m, despite having only modest PFS on ET+CDK4/6i (3, 7, and 12 months respectively). Most frequent all-grade toxicities (tox) were HTN (n = 15, G3:15), hypothyroidism (n = 20, G3:0) and fatigue (n = 13, G3:2), with no G4/5 tox. No new toxicity signals were observed compared to dose escalation phase. Pre-treatment tumor molecular profiling showed responders to be more likely to harbor NEFH, USH2A and PTCH1 mutations, while non-responders were more likely to carry PIK3R1, APC and PALB2 mutations. Sequencing of serial biopsies showed downregulation of BRD4, PTCH1, KIT, NTRK1 and CREBBP after Len treatment. Conclusions: Len+Let showed significant anti-tumor activity with meaningful duration of response, even in pts who failed prior CT or ET+CDK4/6i. The results support further investigation in randomized studies. Tumor profiling identified mutations associated with response and insights on molecular effects of lenvatinib. Clinical trial information: NCT02562118 .

A multicenter study of radiation doses to the eye lenses of medical staff performing non-vascular imaging and interventional radiology procedures in Japan

PurposeThis study aimed to measure the eye lens doses received by physicians and other medical staff participating in non-vascular imaging and interventional radiology procedures in Japan. Material and methodsFrom October 2014 to March 2017, 34 physicians and 29 other medical staff engaged in non-vascular imaging and interventional radiology procedures at 18 Japanese medical facilities. These professionals wore radioprotective lead glasses equipped with small, optically stimulated luminescence dosimeters and additional personal dosimeters at the neck during a 1-month monitoring period. The Hp(3) and the Hp(10) and Hp(0.07) were obtained from these devices, respectively. The monthly Hp(3), Hp(10), and Hp(0.07) for each physician and other medical staff member were then rescaled to a 12-month period to enable comparisons with the revised occupational equivalent dose limit for the eye lens. ResultsAmong physicians, the average annual Hp(3) values measured by the small luminescence dosimeters on radioprotective glasses were 25.5 ± 38.3 mSv/y (range: 0.4–166.8 mSv/y) and 9.3 ± 16.6 mSv/y (range: 0.3–82.4 mSv/y) on the left and right sides, respectively. The corresponding values for other medical staff were 3.7 ± 3.1 mSv/y (range: 0.4–10.4 mSv/y) and 3.2 ± 2.7 mSv/y (range: 0.5–11.5 mSv/y), respectively. ConclusionsThe eye lens doses incurred by physicians and other medical staff who engaged in non-vascular imaging and interventional radiology procedures in Japan were provided. Physicians should wear radioprotective glasses and use additional radioprotective devices to reduce the amount of eye lens doses they receive.

Evaluation of an organ-based tube current modulation tool in pediatric CT examinations

ObjectivesTo investigate the effect of an organ-based tube current modulation (OTCM) technique on organ absorbed dose and assess image quality in pediatric CT examinations.MethodsFour physical anthropomorphic phantoms that represent the average individual as neonate, 1-year-old, 5-year-old, and 10-year-old were used. Standard head and thorax acquisitions were performed with automatic tube current modulation (ATCM) and ATCM+OTCM. Dose calculations were performed by means of Monte Carlo simulations. Radiation dose was measured for superficial and centrally located radiosensitive organs. The angular range of the OTCM exposure window was determined for different tube rotation times (t) by means of a solid-state detector. Image noise was measured as the standard deviation of the Hounsfield unit value in regions of interest drawn at selected anatomical sites.ResultsATCM+OTCM resulted in a reduction of radiation dose to all radiosensitive organs. In head, eye lens dose was reduced by up to 13% in ATCM+OTCM compared with ATCM. In thorax, the corresponding reduction for breast dose was up to 10%. The angular range of the OTCM exposure window decreased with t. For t = 0.4 s, the angular range was limited to 74° in head and 135° for thorax. Image noise was significantly increased in ATCM+OTCM acquisitions across most examined phantoms (p < 0.05).ConclusionsOTCM reduces radiation dose to exposed radiosensitive organs with the eye lens and breast buds exhibiting the highest dose reduction. The OTCM exposure window is narrowed at short t. An increase in noise is inevitable in images located within the OTCM-activated imaged volume.Key Points• In pediatric CT, organ-based tube current modulation reduces radiation dose to all major primarily exposed radiosensitive organs.• Image noise increases within the organ-based tube current modulation enabled imaged volume.• The angular range of the organ-based tube current modulation low exposure window is reduced with tube rotation time.

Radiotherapy for maxillary sinus carcinoma: dosimetric comparison of volumetric modulated arc therapy with 0° and 90° collimator intensity modulated radiation therapy

To compare volumetric modulated arc therapy (VMAT) with 0° and 90° collimator intensity modulated radiation therapy (IMRT) plans for treatment of maxillary sinus carcinomas (MSCs). Eighteen MSC were re-planned for VMAT (two full arcs), 0° collimator 9 beams IMRT (zc-IMRT) and 2 beams with 90° collimator and the remaining 7 beams with 0° collimator IMRT (nc-IMRT). The conformity and homogeneity index (CI and HI) of target volume, dose-volume histogram (DVH) of organs at risk (OARs), and monitor units (MUs) were analyzed. The CI of VMAT with GTV, PTV,1 and PTV2 found significantly more than zc-IMRT and nc-IMRT. The HI of nc-IMRT found significantly smaller than VMAT. In terms of OARs, VMAT significantly reduced the maximum point dose of optic chiasm, the ipsilateral lens, MUs, and the D1% of the ipsilateral lens compared with IMRT. VMAT significantly reduced the maximum point dose of ipsilateral optic nerve, the D1% of optic chiasm, the ipsilateral optic nerve and the mean dose of contralateral eyeball compared with zc-IMRT. For the two IMRT group plans, comparison with zc-IMRT, nc-IMRT could significantly reduce the maximum point dose of ipsilateral lens, the D1% of ipsilateral lens and the MUs. The VMAT has better CI of target volume and could have better OARs sparing effects for optic chiasm, ipsilateral lens and ipsilateral optic nerve compared with IMRT for MSCs. The VMAT also could use fewer MUs and has lower treatment delivery times. The nc-IMRT could have better ipsilateral lens sparing and use fewer MUs compared with zc-IMRT. Therefore we could protect the ipsilateral lens better through changing the angle of the collimator from 0° to 90° when the IMRT technique is used for the treatment of MSCs.

Effect of X-ray protective visors on the eye lens dose during ureteroscopy

Eye lens radiation exposure during fluoroscopy-guided interventional procedures may result in occupational radiation-induced cataracts. We evaluated the eye lens radiation doses and the protective effect of X‑ray protective visors during ureteroscopic procedures. Eye lens doses were measured in front of and behind X‑ray protective visors using eye lens dosemeters during ureteroscopic procedures done by 4different endourologic surgeons within a12-week period. Background radiation dose, simultaneously measured with transport dosemeters, was subtracted. Measured eye lens doses below the detection limit of the eye lens dosemeters were adjusted to the detection limit of 0.028 mSv. Correlating the eye lens doses (ELD) to the dose-area-product (DAP) an ELD/DAP ratio was calculated. Applying this ELD/DAP ratio the potential reduction of the eye lens radiation dose was retrospectively calculated for all ureteroscopic procedures done within one year. Within the 12-week period 76ureteroscopies were done by the 4endourologic surgeons. The accumulated eye lens radiation dose was 0.796 mSv in front of the X‑ray protective visors, and 0.338 mSv behind the X‑ray protective visors. Thus, the eye lens radiation exposure was reduced to at least 42% by using X‑ray protective visors. Considering the 215 documented ureteroscopies in our clinic in the year before starting the study, occupational radiation exposure to the eye lens would have been reduced by X‑ray protective visors from 4.090 to 1.737 mSv. X‑ray protective visors can effectively reduce the radiation exposure to the eye lens during fluoroscopy-guided endourologic procedures and should be used especially by high-volume endourologic surgeons.

Assessment of Eye Lens Dose Reduction When Using Lateral Lead Shields on the Patient's Head during Neurointerventional Fluoroscopic Procedures and Cone-beam Computed Tomography (CBCT) Scans.

The purpose of this study was to evaluate the effect of placing small lead shields on the temple region of the skull to reduce radiation dose to the lens of the eye during interventional fluoroscopically-guided procedures and cone-beam computed tomography (CBCT) scans of the head. EGSnrc Monte-Carlo code was used to determine the eye lens dose reduction when using lateral lead shields for single x-ray projections, CBCT scans with different protocols, and interventional neuroradiology procedures with the Zubal computational head phantom. A clinical C-Arm system was used to take radiographic projections and CBCT scans of anthropomorphic head phantoms without and with lead patches, and the images were compared to assess the effect of the shields. For single lateral projections, a 0.1 (0.3)-mm-thick lead patch reduced the dose to the left-eye lens by 40% to 60% (55% to 80%) from 45° to 90° RAO and to the right-eye lens by around 30% (55%) from 70° to 90° RAO. For different CBCT protocols, the reduction of lens dose with a 0.3-mm-thick lead patch ranged from 20% to 53% at 110 kVp. For CBCT scans of the anthropomorphic phantom, the lead patch introduced streak artifacts that were mainly in the orbital regions but were insignificant in the brain region where most neurointerventional activity occurs. The dose to the patient's eye lens can be reduced considerably by placing small lead shields over the temple region of the head without substantially compromising image quality in neuro-imaging procedures.

Effective dose to patient measurements for flat-detector computed tomography protocols in acute stroke care.

The aim was to measure the effective dose of flat-detector CT (FDCT) whole-brain imaging, biphasic FDCT angiography (FDCT-A), and FDCT perfusion (FDCT-P) protocols and compare it to previously reported effective dose values of multidetector CT (MDCT) applications. We measured effective dose according to the IRCP 103 using an anthropomorphic phantom equipped with thermoluminescent dosimeters (TLDs). Placement was according to anatomical positions of each organ. In total, 60 TLDs (≥ 4 TLDs/organ) were placed into and onto the phantom to account for all relevant organs. Organs within the primary beam were covered with more TLDs. Additionally, we measured dose to the eye lens with two TLDs per eye. Protocols which we routinely use in clinical practice were measured on a biplane angiography system. The effective dose of the 20-s protocol/7-s protocol for whole-brain imaging was 2.6mSv/2.4mSv. The radiation dose to the eye lens was 24/23mGy. For the biphasic high-/low-dose FDCT-A protocol, the effective dose was 8.9/2.8mSv respectively. The eye lens dose was 60/14mGy. The contribution of bolus tracking to the effective dose was 0.66mSv (assuming average duration of 14s). The multisweep FDCT-P protocol had an effective dose of 5.9mSv and an eye lens dose of 46mGy. Except for the high-dose biphasic FDCT-A protocol, FDCT applications used in neuroradiology have effective doses, which do not deviate more than 1mSv from previously reported values for MDCT applications. However, the effective dose to the eye lens in commonly used stroke paradigms exceeds the recommended annual dose twofold. • Flat-detector computed tomography (FDCT) can be used for acute and periinterventional imaging of acute stroke patients and in neurointerventions. • Except for the high-dose FDCT angiography protocol, the effective doses do not deviate more than 1mSv from previously reported values for multidetector CT applications. • Strategies to decrease the effective lens dose especially in younger patients should be evaluated in the future.

Fluoroscopy-guided intervention procedure norms for occupational eye radiation dose: An overall evaluation

The main objective of radiation management in interventional radiology is to minimise the unnecessary use of radiation. Fluoroscopically guided interventional procedures (FGI) are performed with increasing frequency in operating theatre for a growing number of procedures. In this view, we evaluate the occupational eye dose of an interventional radiologist (IR) for different dosimeter positions commonly utilised in the FGI procedures. Herein, one IR was examined for a period of three months while performing the 65 FGI procedures of different types. Eye doses of the IR were measured using the optically-stimulated luminescence dosimeters called the nanoDots (Landauer, Inc.). The IR wore the protective lead glasses equipped with the nanoDots (on the left and right eye) during the observations period. All the nanoDot measurements were conducted using the microStar reader system (Landauer Inc.). The eye dose of the IR per dose area product (DAP) was discerned to be 0.85 ± 0.13 μSv.Gy−1.cm−2 for the left eye with the protection. The estimated annual eye dose of 18.32 mSv.y−1 was below the recommended dose limit (20 mSv.y−1). The mean eye dose and DAP correlation was observed to be significant and insignificantly related to the fluoroscopy time (p < 0.05). The observed lower dose for the right eye than that of the left one was attributed to the specific position of the IR with respect to the patient. Present strategy on the occupational eye dose measurement was shown to be effective for determining the risk of the eye lens dose level in the absence of the protective lead glasses. It is established that the eye dose limit can easily exceed the recommended standard if the IR does not use the protective lead glasses with other safety equipment during the treatment.

CORRELATION OF EYE LENS DOSES AND PERSONAL DOSE EQUIVALENT MEASURED ON THE ARM OF INTERVENTIONAL CARDIOLOGISTS FOR A RETROSPECTIVE ASSESSMENT OF DOSES TO OPERATORS' EYE LENS.

Coefficients converting the readings of the whole body dosemeter worn on the left arm to eye lens doses were determined by analysing the correlations between Hp(10) and Hp(3) values. Doses were measured on a phantom for specific C-arm projections typically used during CA/PCI procedures. In order to estimate the cumulative eye lens doses, conversion coefficients were then applied to the dose records of interventional cardiologists collected in the database of dosimetry service between the years 1995 and 2009. The Hp(10) to Hp(3) conversion coefficients are 0.29 (CV=34%) and 0.17 (CV=42%) for left and right eye lens, respectively. However, they can vary from one laboratory to another depending on working technique. From among 61 interventional cardiologists, none exceeded the threshold dose of 0.5Gy for eye lens opacities. However, 44% of interventional cardiologists were likely to exceed the annual limit of 20mSv for the most exposed eye at least once in the analysed time period.

Comparison of crystalline lens dose rates in interventional cardiology for systems with and without dose optimization software

During the last years, the use of Interventional radiology (IR) has been increasing, because compared to other clinical methods IR techniques are minimal invasive. Nevertheless, these types of surgical procedures are guided by current time images that are produced by X-rays. In the case of interventional cardiology (IC), the complexity of the procedures and production of images that are required expose the medical staff to ionizing radiation. Thus, a dosimetric control of radiation to people who are constantly involved in this type of environment is highly necessary. As most of Latin American countries, Colombia still has not implemented the crystalline lens dosimetry for professionals who are in charge of IR procedures. In addition, if we consider the decrease of the dose limit to the lens Hp(3) from 150 to 20 mSv/year proposed by the ICRP, it is important to take into account this parameter in order to optimize the practice, so the radiological risks to which interventional doctors are exposed can be reduced. In this work we investigated the level of radiation to the lens of 6 doctors dedicated to treat coronary conditions. They belong to 2 clinical centers and have conducted a total of 227 procedures of diagnostic and therapeutic type. The radiation dose measurements were made with thermoluminescent dosimeter (TLD) for both eyes. The results showed that doctors who do not use plumbed glasses exceeded the dose limit for crystalline lens with very few procedures per month. We also found that a recently developed dose optimization software for image processing during angiograph procedures is a factor that strongly reduces the dose to the crystalline lens. Finally, the catheter route (radial or femoral) is an irrelevant factor for the Hp(3) dose to the lens.

Measurement of eye lens doses estimation in interventional radiology

International Commission of Radiological Protection (ICRP) Publication number 118 at 2012 recommends decreasing the Dose Limit Value of eye lens for workers from 150 mSv to 20 mSv in 1 year, and to not exceed 50 mSv in a certain year. This experiments is aimed to evaluate the value of eye lens radiation dose based on the effect of angles on the monitor in interventional radiology by using a head phantom as a simulation of the workers’ position with a height of 150 cm, 160 cm and installed thermoluminescent dosimeter (TLD) chips Hp (10) at 66 - 67 kV and 385 - 395 mA. The radiation lens dose value during 1 minute fluoroscopy irradiation results a mean of radiation dose value that ranges between 0,54 – 0,79 mSv and 0.52 - 0.70 mSv, during 4 minutes fluoroscopy irradiation ranges between 0,48 – 0,72 mSv and 0.55 - 0.75 mSv, and during 10 seconds cinefluorography ranges between 0.52 – 0,75 mSv and 0.48 - 0.66 mSv. The relationship between the linearity of fluoroscopy irradiation time and dose area product (DAP) obtained an equation of y = 0.0139x-0.0535 with a correlation coefficient R2 = 0.9982. The relationship between the linearity of fluoroscopy irradiation time and Kinetic Energy Released per Mass unit (KERMA) obtained an equation of y = 0.0957x-0.0495 with a correlation coefficient R2 = 0.9988.

Development of Detailed Korean Adult Eye Model for Lens Dose Calculation

Development of Detailed Korean Adult Eye Model for Lens Dose Calculation

Eye Lens Dosimetry in Interventional Radiology: Assessment With Dedicated Hp(3) Dosimeters.

To quantify eye lens dose in interventional radiology and assess whether neck dosimeter is a good surrogate to evaluate eye lens dosimetry. Radiation exposure was prospectively measured in 9 interventional radiologists between May and October 2017. Standard Hp(0,07) thermoluminescent dosimeters (TLDs) were worn at the neck outside the lead apron, and 2 dedicated eye lens Hp(3) TLDs were placed just above the eyes, one midline and another at the outer edge of the left eye. Correlations between eye lens and neck TLD doses were assessed with Pearson coefficient, and linear regression was used to predict eye lens dose from neck TLD values. Eye lens dose without eye protection was 0.18 ± 0.11 (mean ± standard deviation; 0.08-0.41) mSv per workday and 35.3 ± 6.6 mSv (16.3-82.9) annually (200 workdays/year). Five (56%) radiologists exceeded the 20 mSv annual eye lens dose limit. Eye lens doses from left and central TLDs were 12.46 ± 3.02 and 9.29 ± 3.38 mSv, respectively (P = .027). Mean eye lens (left and central) and neck TLD doses were 10.87 ± 2.67 and 16.56 ± 5.67 mSv, respectively (P = .008). Pearson correlation coefficient between both eye lens TLD and between mean eye lens TLD and neck TLD doses were 0.91 and 0.92, respectively. Average of eye lens dose was 0.0179 + (0.5971 × neck dose). Full-time interventional radiologists are likely to suffer from deterministic radiation effects to the eye lens, especially on the left side. Neck TLD significantly overestimates eye lens dose. However, eye lens doses are highly correlated with neck doses and may be predicted from the neck TLD values.

Eye lens dosimetry for workers at Fukushima Daiichi Nuclear Power Plant—2: Field study using humanoid phantoms

We performed a field study of eye lens dosimetry for workers involved in the decommissioning operation at the Fukushima Daiichi Nuclear Power Plant. In this study, humanoid phantoms equipped with different personal dosemeters were placed at selected locations in the workplace. The experiment showed that Hp(3) at the head is about 20% higher than Hp(10) (or Hp(3)) at the trunk. This level of dose gradient is generally interpreted as being “almost uniform” in radiological control; therefore, tasks conducted in open areas with such relatively small dose gradients (~1.2) will not require specific monitoring with eye lens dosemeters, except when the eye lens dose approaches the dose limit.

Peak skin and eye lens radiation dose from brain perfusion CT: CTDIvol and Monte Carlo based estimations

PurposeTo quantify the eye lens, peak skin and brain doses associated with head CT perfusion exam by means of thermoluminescent dosimeters (TLDs) measurements in a cadaver and compare them to Monte Carlo (MC) dose estimations as well as to the CTDIvol. Method18 TLDs were inserted in the brain, skin, and eye lenses of a female cadaver head, who underwent a CT brain perfusion scan using a Siemens Definition Flash. The table-toggling protocol used 80 kVp, 200 mAs, 32 × 1.2 mm collimation and 30 sequences. From the CT images, a voxel model was created. Doses were calculated with a MC framework (EGSnrc) and compared to TLD measurements. TLD measurements were also compared to the displayed CTDIvol. ResultsThe average measured doses were: 185 mGy for the eyes lenses, 107 mGy for the skin, 172 mGy for the brain and 273 mGy for the peak skin. The reported CTDIvol of 259 mGy overestimated the averaged organ doses but not the peak skin dose. MC estimated organ doses were 147 mGy for the eyes (average), 104 mGy for the skin and 178 mGy for the brain (-20 %, -3% and 4% difference respect to the TLDs measurements, respectively). ConclusionsCTDIvol remains a conservative metric for average brain, skin and eyes lenses doses. For accurate eye lens and skin dose estimates MC simulations can be used. CTDIvol should be used with caution as it was of the same order of magnitude as the peak skin dose for this protocol and this particular CT scanner.

Air-kerma to Hp(0.07), Hp(3), and Hp(10) conversion coefficients for monoenergetic photons

This work aims for calculating a new set of the personal dose equivalent conversion coefficients Hp(d)/Kair when d = 0.07, 3, and 10 mm, for monoenergetic photons beams ranged from 0.015 to 10 MeV, which have incident on ICRU slab phantom for Hp (0.07) and Hp (10) and cylindrical phantom for Hp (3). The new cylindrical phantom of the ORAMED project was proposed for calculating the eye lens dose equivalent as a cylinder much better approximates the form of a head than a slab. The calculations were carried out with MC and an analytical fit is applied to the data. Our results are found in a good agreement with those previously published, with a local difference less than 1.5%. We have concluded that new analytical fits provide a suitable method for determining conversion coefficients for discrete incident such as MC.

Measurement of the Whole Body, Eye Lens and Extremity Occupational Doses in Nuclear Medicine Staff at King Chulalongkorn Memorial Hospital

Nuclear medicine staff have handled several radionuclides of gamma and beta emitters which result in obtaining occupational radiation risk. In 2018, the Government of Thailand announced the reduction of the eye lens dose limit from 150 to 20 mSv per year for the consecutive 5 years as of ICRP No. 118 in 2011. In Thailand, the personal effective dose to whole body, Hp(10) and the personal equivalent dose to the extremity, Hp(0.07) have been measured using optically stimulated luminescence dosimeter (OSLD) in nuclear medicine staffs while the personal equivalent dose to the eye lens, Hp(3) has never been measured. The objective is to measure Hp(10), Hp(3), and Hp(0.07) using OSLD in nuclear medicine staff who dispense high activity of radionuclides at King Chulalongkorn Memorial Hospital (KCMH). The correlations between the Hp(10), Hp(3) and Hp(0.07) were analyzed. The personal occupational dose has been measured in 10 nuclear medicine staff. Three sets of OSLD are attached at whole body, finger, and eye lens (left and right) of each personnel arranged by Thailand Institute of Nuclear Technology (TINT). As some radionuclides emit beta and gamma, most staff perform best practice in routine work, the short exposure time and the short range of beta rays to reach eye dosimeters which result in the estimated annual whole body, eye lens and extremity were less than the annual dose limit. The correlations between Hp(3) and Hp(10), Hp(0.07) and Hp(10), Hp(3) and Hp(0.07) had been recorded, while Hp(3) could be estimated from Hp(10).